1. Field of the Invention
The present invention relates to a sealing device for a universal joint, and the sealing device seals a bearing portion of the universal joint used as a connection means for a propeller shaft, a steering shaft, or the like of an automobile.
2. Description of the Conventional Art
A universal joint in a propeller shaft or the like of an automobile is structured such that a yoke provided at a shaft end of a driving side rotary shaft and a yoke provided at a shaft end of a driven side rotary shaft are mutually angle-displaceably connected through a cruciform spider, and rotating force is transmitted from the driving side to the driven side through the cruciform spider. Each of four shaft portions, which project to be mutually cruciformly, of the cruciform spider is inserted into a connection hole through a needle bearing, where the connection hole is provided in a fork-shaped arm of the driving side or driven side yoke. The needle bearing is sealed by a sealing device to prevent grease sealed inside the bearing from leaking, and prevent muddy water from invading from the outside.
Each of FIGS. 8 and 9 is a half sectional view of an installation state of a sealing device for a universal joint for illustrating a typical conventional technique. FIG. 10 is a half sectional view for illustrating an installing process of the sealing device illustrated in FIG. 8.
In FIGS. 8 and 9, a referential numeral 110 denotes a cruciform spider of a universal joint. A needle bearing 120 includes an outer ring 121 and many cylindrical rolling elements 122. The outer ring 121 is freely arranged at a shaft portion 111 of the cruciform spider 110, and fitted to a connection hole of a yoke not illustrated. The plurality of cylindrical rolling elements 122 is put between the outer ring 121 and the shaft portion 111. In addition, the needle bearing 120 illustrated in FIG. 8 is a comparatively small one for a passenger car, and the outer ring 121 is a comparatively thin part made of a press-molded product. The needle bearing 120 illustrated in FIG. 9 is for a large vehicle, such as a truck, and the outer ring 121 is a comparatively thick part made of a cast product.
A sealing device 100A illustrated in FIG. 8 is attached to the shaft portion 111 of the cruciform spider 110 since the outer ring 121 of the needle bearing 120 is comparatively thin. The sealing device 100A has a plurality of seal lips 102 and 103 and an inner peripheral seal portion 104 at an end of the outer ring 121. These seal lips 102 and 103, and the seal portion 104 are made of a rubber like elastic material and integrally formed with a metal ring 101 (for example, refer to Japanese Patent Application Laid-Open No. 11-125338). A plurality of the seal lips 102 and 103 comes into slidably close contact with a rounded surface of an inward bending portion 121a which is bent by pressing in order to prevent the cylindrical rolling elements 122 from falling out. The inner peripheral seal portion 104 is press-fitted on an outer peripheral surface of the shaft portion 111.
On the other hand, a sealing device 100B illustrated in FIG. 9 is pressed in to be attached to the outer ring 121 of the needle bearing 120. That is, the sealing device 100B has a plurality of seal lips 106 to 108, which are made of a rubber like elastic material and integrally formed with a metal ring 105 (for example, refer to Japanese Patent Application Laid-Open No. 2006-118662 and Japanese Patent Application Laid-Open No. 2006-162079). The metal ring 105 is press-fitted on an inner peripheral surface of an end of the outer ring 121. The plurality of the seal lips 106 to 108 comes into slidably close contact with a curved surface 110a and a near part of the curved surface 110a. The curved surface 110a is formed from the shaft portion 111 of the cruciform spider 110 to a boss portion 112.
Reference is made to Japanese Patent Application Laid-Open No. 11-125338, Japanese Patent Application Laid-Open No. 2006-118662 and Japanese Patent Application Laid-Open No. 2006-162079.
However, in the sealing device 100A illustrated in FIG. 8, the inward bending portion 121a of the outer ring 121 which is close contacted with the seal lips 102 and 103 is formed by pressing work. Thus, the accuracy of curvature of the rounded surface is low, and close contact surface pressure of the seal lips 102 and 103 varies greatly. Therefore, the sealing device 100A has a problem that muddy water sealing performance is instable. Further, as illustrated in FIG. 10, when the sealing device 100A is press-fitted on the shaft portion 111 of the cruciform sper 110 by using a jig 200, the seal lip 102 is necessarily to be pressed, so that the sealing device 100A could be damaged because the seal lip 102 is crushed.
On the other hand, the sealing device 100B illustrated in FIG. 9 is press-fitted to the inner peripheral surface of the end of the outer ring 121 of the needle bearing 120. When the outer ring 121 is made of a press-molded product, the outer ring 121 could be deformed by pressing. Thus, the outer ring 121 is made of a comparatively thick cast product. However, a fitted portion with the metal ring 105 is positioned outside the seal portions with the seal lips 106 to 108. In addition, since the outer ring 121 is made of the cast product, the surface of the outer ring 121 is rough. Therefore, the muddy water sealing performance of the fitted portion with the metal ring 105 could be insufficient. Further, in order to obtain sufficient muddy water sealing performance with the seal lips 106 to 108, the positioning accuracy of the sealing device 100B with respect to the curved surface 110a needs to be high.